An upper-bearing typed movable formwork is construction equipment for bridge superstructure construction, and especially applicable to production of a concrete simple box girder or continuous box girder. According to different relative positions of an upper-bearing typed movable formwork main girder and the concrete box girder, the upper-bearing typed movable formwork is classified into a deck type and a through type, in which the main girder of the through upper-bearing typed movable formwork is located above the concrete box girder, and the main girder of the upper-bearing typed movable formwork is located below the concrete box girder. Compared with the through upper-bearing typed movable formwork, the upper-bearing typed movable formwork has the advantages of an open working plane and no additional load generated on the concrete box girder when the scaffolding system runs through holes, and is widely applied in engineering practice. For the conventional upper-bearing typed movable formwork, the main girder is located below the concrete box girder; generally, one girder is disposed at two sides of a pier shaft respectively, a transverse truss (or a transverse steel box girder) is usually disposed at the top or one side of the main girder, a formwork system is disposed on the top of the transverse truss (or the transverse steel box girder), and the load (the dead weight of the concrete box girder, and the side pressure of the newly-cast concrete, and so on) of the upper-bearing typed movable formwork is transferred to the transverse truss (or the transverse steel box girder) through the formwork system, and then is transferred onto the main girder of the upper-bearing typed movable formwork.
The technical solution of the conventional upper-bearing typed movable formwork has the following disadvantages:
(a) Large dead weight: firstly, since the formwork system is disposed on the top of the transverse truss (the transverse steel box girder), the rigidity of the formwork system cannot be fully utilized, and the transverse truss (the transverse steel box girder) needs to bear the entire load, which requires the transverse truss to have a great rigidity and a large dead weight; additionally, the deformation value of the upper-bearing typed movable formwork is a sum of the deformation values of the formwork system, the transverse truss (the transverse steel box girder), and the main girder, and thus the structure deformation is great and relatively soft, and in the condition of the same rigidity, the upper-bearing typed movable formwork needs to consume more steel.
(b) High occupation space: below the bottom surface of the concrete box girder, the height of the occupation space of the conventional upper-bearing typed movable formwork is a sum of heights of structures such as the bottom formwork system, the transverse truss (the transverse steel box girder), the main girder, the vertical and horizontal transfer system, and a landing leg; when the height of the pier shaft is close to and even smaller than the sum of the heights, the upper-bearing typed movable formwork operation is difficult, and even cannot be implemented. Low pier shafts are usually used in passenger railway bridges in China.
(c) Unreasonable structure stress: the deployment of the structural system of the conventional upper-bearing typed movable formwork determines the disadvantages that the transverse truss (the transverse steel box girder) is bent, the load of web plates at the inner and outer sides of the girder is not even, and the additional torque is great, and the structure stress is unreasonable, thus resulting in increase of the dead weight of the structures and increase of risks.
(d) Many horizontal transfer mechanisms and complicated operations: for the conventional upper-bearing typed movable formwork, the transverse truss (the transverse steel box girder) and formwork system are divided into several individual action units longitudinally, each unit is equipped with a set of horizontal transfer mechanisms, and when the upper-bearing typed movable formwork runs, the horizontal transfer mechanisms are operated respectively, so that the action units are traversed one by one. The technical solution needs many horizontal transfer mechanisms and many procedures.